1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device in which an adhesive force between an upper substrate and a lower substrate is enhanced.
2. Description of the Related Art
Generally, a liquid crystal panel of the LCD includes a lower substrate on which thin film transistors are arranged and an upper substrate on which a color filter is formed. Between the upper substrate and the lower substrate, a liquid crystal is positioned. A common electrode is formed on an inner surface of the upper substrate facing the lower substrate. Pixel electrodes are formed on an inner surface of the lower substrate facing the upper substrate. Thus, the common electrode and the pixel electrodes are arranged to face with each other. The liquid crystal is interposed into a space between the upper and lower substrates through an injection opening of a seal about the periphery of the upper and lower substrates. The injection opening is sealed after the liquid crystal is interposed between the upper and lower substrates. Subsequently, polarizing plates are attached to outer surfaces of the upper substrate and the lower substrate to complete the LCD device.
The light transmission of each LCD device in a liquid crystal display panel is controlled by applying voltages to each of the pixel electrodes with respect to the common electrode such that characters/images are displayed on the liquid crystal display panel via an optical shutter effect in each of the LCD devices.
FIG. 1 is a plan view schematically showing a structure of the related art liquid crystal display panel. As shown in FIG. 1, the related art liquid crystal display panel 2 has a lower substrate 4 and an upper substrate 6 configured to be in parallel and face each other. Between the lower substrate 4 and the upper substrate 6 of the related art liquid crystal display panel 2, an image display part 8 has liquid crystal cells arranged in a matrix configuration. A gate pad 12 and a data pad 14 are connected between driving ICs (not shown) and the image display part 8. A gate link 34 and a data link 16 connect the gate pad 12 and the data pad 14 to the image display part 8, respectively. A seal pattern 10 is formed on an outer periphery of the image display part 8 such that the lower substrate 4 is adhered to the upper substrate 6.
In the image display part 8, a plurality of data lines 13 through which video signals are applied via the data pad 14 and the data link 16, and a plurality of gate lines 11 through which gate signals are applied via the gate pad 12 and the gate link 34 are arranged on the lower substrate 4 such that the data lines and gate lines cross over each other. Each of the liquid crystal cells is positioned adjacent to where data line and gate line cross over each other. In addition, each of the liquid crystal cells has a Thin Film Transistor (“TFT”) for switching a data signal to a pixel electrode connected to the TFT so as to drive the liquid crystal cell.
The upper substrate 6 includes red (R), green (G) and blue (B) color filters formed in separate liquid crystal cells that are separated by a black matrix. A transparent conductive electrode is formed on the surface of the color filters as a common electrode. The upper substrate 6 and the lower substrate 4 are spaced apart from each other by a spacer to maintain a cell gap of a predetermined interval. This cell gap together with the seal pattern 10 defines the region into which the liquid crystal is injected after the upper substrate 6 and the lower substrate 4 are adhered to each other. The upper substrate 6 and the lower substrate 4 are attached to each other by a sealant that is coated on as a seal pattern 10 on the outer periphery of the image display part 8. Liquid crystal is injected in between the upper substrate 6 and the lower substrate 4 through an injection opening, and the injection hole is sealed.
The gate pad 12 and the data pad 14 are formed along a periphery of the lower substrate 4 that is not overlapped by the upper substrate 6. The gate pad 12 supplies the gate lines 11 of the image display part 8 via the gate link 34 with a scan signal provided from the gate drive IC (not shown) through interconnection lines of a tape carrier package (TCP) film (not shown). Also, the data pad 14 supplies the data lines 13 of the image display part 8 via the data link 16 with a video data signal provided from a data drive IC (not shown).
In the liquid crystal display panel 2 of FIG. 1, a passivation film for protecting metal electrode lines and thin film transistors on the lower substrate 4 from the liquid crystal is coated on the entire upper surface of the lower substrate 4 facing the upper substrate 6. Pixel electrodes are connected to the thin film transistors of the liquid cells through contact holes formed in the passivation film of every liquid crystal cell. The pixel electrode is a transparent conductive electrode, such as Indium Tin Oxide (“ITO”), and has a comparatively strong endurance property against the liquid crystal material.
An inorganic insulating film such as SiNx or SiOx is typically used as a passivation film. However, an inorganic passivation film has of high dielectric constant. Accordingly, a coupling effect can occur due to a parasitic capacitance formed between the pixel electrode and the data lines 13 with the inorganic passivation film therebetween. Hence, when an inorganic passivation film is used, the pixel electrode and the data lines 13 are spaced far apart from each other by a comparatively long distance of 3˜5 μm so that they do not to overlap with each other and to minimize such a coupling effect. Thus, the area of the pixel electrode, which applies voltage to the liquid crystal layer, has to be made smaller, which adversely affects the aperture ratio of the liquid cell in that less of the overall area of the liquid crystal cell is used.
To overcome this adverse affect to the aperture ratio, an organic material that has a comparatively low dielectric constant, such as Benzocyclobutene (BCB), Spin on glass (SOG), Acryl or the like, is used as the passivation film. Since such an organic material has a low dielectric constant of about 2.7, a pixel electrode can be overlapped with a data line to some degree. Accordingly, the aperture ratio of the liquid crystal cell can be improved corresponding to the increase in the area of the pixel electrode as result of overlapping a pixel electrode with a data line.
In an LCD having a high aperture ratio and provided with an organic passivation film, the sealant coated as the seal pattern 10 contacts the organic passivation film of the lower substrate 4 when attaching the upper substrate 6 and the lower substrate 4 to each other. However, the sealant is mainly made of an epoxy resin or the like having a weak adhesive bonding characteristic to the organic passivation film while it has a strong adhesive bonding characteristic to glass and an inorganic passivation film. Thus, in a liquid crystal display having a high aperture ratio provided with an organic passivation film, liquid crystal may leak from a seal pattern 10 that has a weak adhesive force between the sealant and the organic passivation film when the liquid crystal display panel is impacted or subjected to other kinds of increased pressure. In addition, the organic passivation film has a bad adhesive bonding characteristic to the gate insulating film formed below the organic passivation film. Thus, even a slight amount of pressure may easily create a break between the organic passivation film and the gate insulating film very easily, so that the organic passivation film is delaminated or the liquid crystal leaks.
FIG. 2 is a magnified plan view of the cross portion between the data link and the seal pattern of the related art LCD shown in FIG. 1. As shown in FIG. 2, the data link 16 is formed together with the data pad 14 and the data line 13 in the image display part. Below the data link 16, the semiconductor layer 18 is formed extending from the data line 13 to the data pad 14. The semiconductor layer 18 is formed below the data link 16 in a fabrication method using four (4) masks. The semiconductor layer 18 may not be formed below the data link 16 in a fabrication method using five (5) masks. Also, FIG. 2 illustrates that the seal pattern 10 of sealant is formed to cross the data link 16 on the organic passivation film at a crook in the data link 16.
The data pad 14 is contacted to a transparent electrode 17 on the organic passivation film through a contact hole 19 formed in the organic passivation film. Here, the transparent electrode 17 connected to a data drive IC mounted on a TCP film functions to protect a metal electrode that is a data pad 14 and also prevents the metal electrode from being oxidized when repeating an adhering process of the TCP film that is required in a TAB procedure.
FIG. 3A is a vertical sectional view of a liquid crystal panel taken along the line I-I′ of FIG. 2, and FIG. 3B is a vertical sectional view of a liquid crystal panel taken along the line II-II′ of FIG. 2. Referring to FIGS. 3A and 3B, the lower substrate 4 is constructed to include a gate insulating film 22, a semiconductor layer 18 and a data link 16 that are stacked in this named order on a glass substrate 20. Organic passivation film 24 is formed to cover the entire surface of the gate insulating film 22 including the semiconductor layer 18 and the data link 16.
The upper substrate 6 is configured to include a color filter, a black matrix 28 and a transparent common electrode 26 that are formed in this named order on the rear surface of an upper glass substrate 30 facing the lower substrate 20. The transparent common electrode 26 is formed on the entire rear surface of the upper glass substrate 30. The lower substrate 4 and the upper substrate 6 are attached to each other by the sealant coated as the seal pattern 10.
In this case, the sealant of the seal pattern 10 is adhered to the organic passivation film 24 and has a weak adhesive bonding force. In addition, the organic passivation film 24 very weakly adheres to the gate insulating film 22 that is made of inorganic material and formed below the organic passivation film 24. Thus, a crack may be created by an external impact such that the organic passivation film 24 may delaminate or the liquid crystal will leak out. As shown in FIG. 3B, the region inside the seal pattern 10 is in the image display part 8 where the liquid crystal 32 is injected.
FIG. 4 a magnified plan view of a portion of a gate link crossing the seal pattern shown in FIG. 1. As shown in FIG. 4, the gate link 34 is formed together with the gate pad 12 and the gate line 11 of an image display part. The gate pad 12 is connected to the transparent electrode 17 through the contact hole 19 formed in the gate insulating film and the overlying organic passivation film. Also, FIG. 4 illustrates that the seal pattern 10 of sealant is formed to cross the gate link 34 on the organic passivation film at a crook in the gate link 34.
FIG. 5A is a vertical sectional view of a liquid crystal panel taken along the line III-III′ of FIG. 4, and FIG. 5B is a vertical sectional view of a liquid crystal panel taken along the line IV-IV′ of FIG. 4. Referring to FIGS. 5A and 5B, a lower substrate 4 is configured to include a gate link 34, a gate insulating film 22, and an organic passivation film 24 that are stacked in this named order on a glass substrate 20. The organic passivation film 24 is formed to cover the entire surface of the glass substrate 20 including the gate insulating film 22.
Like in the case of the data link above, the sealant of the seal pattern 10 adheres to the organic passivation film 24 with a weak adhesive bonding force. Further, in the area on which the seal pattern 10 is formed other than adjacent to the data pad 14 and the gate pad 12, the sealant of the seal pattern 10 is also adhered to the organic passivation film 24 with a weak adhesive bonding force. As an overall result, a liquid crystal display panel having a high aperture ratio using an organic passivation film has a weak adhesive bonding force between the sealant and the organic passivation film as well as between the organic passivation film and the gate insulating film that may result in a liquid crystal leak.